The present invention relates to a thin film transistor liquid crystal display (TFT LCD), and particularly, to a TFT LCD panel.
In producing of a TFT LCD, electrostatic is always induced for example during production, testing, and transporting. Friction and contact may generate an instantaneous voltage up to thousands of voltages and generate a large current of about 20 amperes. However, a glass substrate for the TFT LCD is non-conductive and is not favorable for release of the electrostatic. Electrostatic accumulation (ESC) and electrostatic discharging (ESD) are prone to breakdown insulating layers on the substrate and directly result in a short circuit or partial damage, thus reducing yield.
In addition, to improve the production efficiency during producing of a TFT LCD, Au balls (in general, formed of plastic particles coated with a Ni or Au layer) are used in design for many products, and the Au balls can replace the conventional conductive Ag adhesive. Au balls communicate the common electrode for a color filter substrate and the common electrode for an array substrate, thus decreasing process steps and improving the production efficiency. However, the common electrode (usually made of indium tin oxide (ITO)) on the color filter substrate tends to induce electrostatic breakdown with a data-line wiring or a gate-line wiring via the Au balls and form a data-line or gate-line bright line (also called an X or Y bright line in the art), certain reason for which lies in that the external electrostatic induced during production breaks down the protection layer on the data-line wiring or the gate-line wiring so that the data-line wiring or the gate-line wiring and the common electrode on the color filter substrate are conducted via the Au balls.
In the conventional design, Au balls are directly mixed in the sealant for coating. Au balls are particles dispersed in the sealant and are pressed during the assembly process between the array substrate and the color filter substrate, in which Au balls contacts the common electrode of the color filter substrate and the common electrode of the array substrate to establish a conduction path therebetween. Such process is similar to Ag adhesive electrode in the conventional assembly process. In this process, Au balls will directly contact the protection layer in a data-line wiring region or a gate-line wiring region, and the electrostatic during the process may easily breaks down the protection layer. The breakdown mentioned above occurs in the conventional process at a probability of about 1% and reduces the yield.
FIG. 1 is a structure diagram showing a conventional TFT LCD. As shown in FIG. 1, the TFT LCD comprises an array substrate and a color filter substrate, which are bonded together with a sealant (mixed with Au balls therein) 4 to form a panel. Between the edge of the array substrate 1 and the edge of the color filter substrate 3, there are provided a plurality of patterned pads 2 for data-line signal output and connected with data-line wirings. Also, there are provided a plurality of patterned pads for gate-line signal output and connected with gate-line wirings on the array substrate, which are not shown in FIG. 1. After being led out from a display region 8 of the array substrate, the data-line wirings 6 are connected with the patterned pads 2 for data-line signal output. Data-line signals pass over the patterned pads 2 for data-line signal output and the data-line wirings 6 of the TFT LCD panel via the peripheral circuit and enter the display region for image displaying.
FIG. 2 is an enlarged view of the portion indicated by a reference numeral 7 in FIG. 1, and FIG. 3 is a cross-sectional view taken along line A-A in FIG. 2.
With reference to FIGS. 2 and 3, portions of the data-line wirings 6 on the array substrate 15 and those of the common electrode 13 on the color filter substrate 11 overlap each other and contact via Au balls 14 in sealant 4. In this situation, only a protection layer 12 over the data-line wirings 6 acts as an isolation layer (FIG. 2). After the assembly process, the sealant 4 with Au balls 14 is pressed to conduct the common electrodes on the upper and lower substrates. When the sealant 4 with Au balls 14 are pressed, the Au balls 14 and the protection layer 12 fully contact with each other; however, the thickness of the protection layer 12 formed over the data-line wirings 6 is only about 0.3 μm. Therefore, under a strong electric field between the applied data-line signals and the common electrode signals, the protection layer 12 is prone to be broken down. Once the protection layer 12 is broken down, a short circuit forms between the common electrode on the color filter substrate and the data-line wirings in the overlapping portions, which induces poor display quality. The electrostatic breakdown portion is illustratively indicated with the reference number 10 in FIGS. 2 and 3, where the electrostatic breakdown occurs. In a same way, short circuit between the common electrode on the color filter substrate and the gate-line wirings in the overlapping portions may occur and lead to poor display quality, which is not described herein for simplicity.
In addition, in the conventional technique, a black matrix of the color filter substrate forms an integral structure outside the display region, and the common electrode is formed with a blanket deposition process. Therefore, the black matrix needs one mask process during formation, and the common electrode needs no mask process in formation. That is to say, in the portion where the common electrode on the color filter substrate and a data-line wiring or a gate-line wiring overlap each other, it is inevitable for the common electrode on the color filter substrate to directly contact the protection layer on the data-line wirings or the gate-line wirings by using Au-balls.